Compositions and methods for high-efficiency cleaning of semiconductor wafers

ABSTRACT

A composition including supercritical fluid and at least one additive selected from fluoro species, and primary and/or secondary amines, optionally with co-solvent, low k material attack-inhibitor(s) and/or surfactant(s). The composition has particular utility for cleaning of semiconductor wafers to remove post-ashing residues therefrom.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of the U.S. patent application Ser. No.10/602,172 for “Compositions and Methods for High-Efficiency Cleaning ofSemiconductor Wafers” filed on Jun. 24, 2003 in the name of Michael B.Korzenski et al., which is incorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to compositions and methods forhigh-efficiency cleaning of semiconductor wafers.

DESCRIPTION OF THE RELATED ART

The fabrication of multi-layer semiconductor circuits requires thedeposition of multiple patterned layers of semiconductor, conductor anddielectric materials. Patterning is conventionally carried out byoptical imaging of a photoresist layer formed from a compositioncontaining a soluble polymer and a photoactive compound. Followingpatterning, deposition, and etching, the photoresist layer must becompletely removed before the next processing step.

Plasma ashing can remove photoresist but leaves a post-ash residue onthe substrate that must be removed. Typically, liquid photoresist orpost-ash residue removers are employed. Such removers, however, generatea large amount of hazardous waste that is harmful to the environment,and costly to dispose of, or treat.

The art therefore has a continuing and critical need for improvedcompositions for cleaning of residues, e.g., post-ashing residues, fromsemiconductor wafers (such term herein including wafer base or substratearticles per se, as well as such articles having material depositedthereon or therein to form semiconductor devices or precursor structuresfor such devices.

As a further and specific problem attendant the use of conventionalliquid-based cleaning and post-etch residue removal compositions, thegeometric scale of features in semiconductor device architecturescontinues to diminish. At critical dimensions (of high aspect ratiovias, deep trenches and other semiconductor device or precursorstructure features) below 0.1 μm, the high surface tension that ischaracteristic of aqueous compositions used to clean wafers prevents thepenetration of the composition into the semiconductor wafer features.

Thus, although liquid-based cleaning and post-etch residue removalintegrated circuit processes are well-developed and accepted for devicemanufacturing, their future utility is highly questionable. Apart fromproblems attendant the high surface tension of aqueous cleaningcompositions, copper, porous, low-k multi-layers may require special,non-aqueous cleaning to eliminate aqueous contamination of the pores andconsequent reduction of device yields when pore contaminants cannot beremoved. Additionally, the dielectric constant of low k materials iscritical and aqueous contamination can negatively increase thedielectric constant.

The foregoing highlights the need of the art for improved cleaningcompositions and methods for removal of post-etch lithographic resist(polymer) residue, removal of chemical mechanical planarization (CMP)particles in deep-trench, high aspect ratio vias, removal of metaloxides, metal residues and metal contaminants that remain on the waferafter etching, CMP and interconnect processes (e.g., physical vapordeposition (PVD), chemical vapor deposition (CVD) and plating) formetalization.

SUMMARY OF THE INVENTION

The present invention relates to compositions and methods forhigh-efficiency cleaning of semiconductor wafers.

In one aspect, the invention relates to a composition for cleaningsemiconductor wafers, wherein the composition includes a supercriticalfluid and at least one additive selected from the group consisting of:

a. fluoro-species; and

b. primary and/or secondary amine(s).

Another aspect of the invention relates to a method of cleaning of asemiconductor wafer, wherein the method comprises contacting thesemiconductor wafer with a supercritical fluid-based cleaningcomposition including supercritical fluid and at least one additiveselected from the group consisting of:

a. fluoro-species; and

b. primary and/or secondary amine(s).

Other aspects, features and embodiments of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscope (SEM) micrograph of apost-ashing trench structure in a two-layer coating on a siliconsubstrate, wherein the two-layer coating includes a first (lower) layerof low k dielectric material and a second (upper) layer of a cappingdielectric material, before cleaning.

FIG. 2 is an SEM micrograph of the trench structure of FIG. 1, afterwashing with a cleaning composition comprising SCCO₂, ethanol,(C₂H₅)₃N(3HF) and boric acid.

FIGS. 3A and 3B are scanning electron microscope (SEM) micrographs of apost-ashing trench structure in a two-layer coating on a siliconsubstrate, wherein the two-layer coating includes a first (lower) layerof low k dielectric material and a second (upper) layer of a cappingdielectric material, before cleaning.

FIG. 4 is an SEM micrograph of the trench structure of FIG. 1, afterwashing with a cleaning composition comprising SCCO₂, isopropanol, NH₄Fand non-ionic surfactant.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

The present invention relates to compositions and methods forhigh-efficiency cleaning of semiconductor wafers. The compositionsinclude supercritical fluid and at least one additive selected from thegroup consisting of (I) fluoro-species and (II) primary and/or secondaryamine(s). Such compositions optionally further include co-solvent, low kmaterial-attack-inhibitor, and/or surfactant species, as variouslyemployed in specific embodiments of the invention.

In general, the compositions of the invention as variously hereinafterdescribed may alternatively “comprise,” “consist” or “consistessentially of” the ingredients specified for such compositions.Additionally, compositions of the invention can further includestabilizers, dispersants, etc., and other ingredients, as appropriate tothe formulation and use of such compositions.

In one aspect, the invention provides wafer-cleaning compositionsutilizing a supercritical fluid (SCF) in combination with hydrogenfluoride and/or a fluoride ion source.

The invention in such aspect utilizes a supercritical fluid componenthaving the viscosity and diffusivity of a gas, and thereby capable ofpenetrating quickly into interstices, trenches, high aspect ratio vias,and other finely-dimensioned features of the wafer article. Thesupercritical fluid comprises a substantial major fraction of thecleaning composition. The cleaning composition also compensates for thepolarity of the SCF by inclusion of a component having a polarity thatis opposite to that of the SCF. For example, the non-polar character ofa SCCO₂ component is compensated by incorporation of a hydrogen fluoride(HF) and/or fluoride ion

(F) component, hereafter referred to as “fluoro species,” so that theSCF's inherently low ability to solubilize polymer and/or post-ashresidues is obviated by the presence of the fluoro species, whichimparts to the composition the capability to solubilize polar surfaceresidues on the semiconductor wafer, and to increase the etch rates ofaqueous as well as non-aqueous solutions.

It is indeed surprising that SCF and fluoro species in combination wouldbe an effective cleaning combination for photoresist and post-ashingresidues on the semiconductor wafer, since fluoro species exhibit verylow solubilities in SCF media, and since it would be expected that theSCF would be such an effective penetrant as to blanket the wafer surfacepreferentially and produce only a low level, if any, of polymer and/orpost-ashing residue from the wafer surface, so that any removal actioncaused by chemical (etching) attack on the wafer surface would benegligible or energetically disfavored. This however, has beendiscovered to not be the case. Contrariwise, the combination of SCF andfluoro species has been demonstrated to be an effective cleaningcombination having superior ability to remove polymer resist materialsas well as post-ash residues from the wafer surface.

SCF/fluoro species compositions of the invention are readily formulatedfor use in cleaning of oxides and oxide-containing residues, bysubjecting the source fluid for the SCF to pressure and temperatureconditions above the critical point where the source fluid becomes asupercritical fluid. Once the source fluid is in the SCF state, thefluoro species and optional other ingredients of the composition areadded, e.g., under simple mixing or blending conditions to produce ahomogeneous cleaning composition.

Such optional other ingredients include co-solvent media (to enhance thesolubility of the fluoro species in the SCF), inhibitors (to prevent orat least minimize attack of the cleaning composition on low k and othersusceptible materials on the wafer surface), surfactants (to increasethe homogeneity of the composition and the compatibility of its blendedcomponents), and other additives, adjuvants and enhancers such as may beuseful or desirable in a given cleaning operation.

The SCF used in compositions of the invention can be of any suitabletype. Non-limiting examples of SCF species that can be used in the broadpractice of the invention include carbon dioxide, oxygen, argon,krypton, xenon, ammonia, methane, methanol, dimethyl ketone, hydrogen,forming gas, and sulfur hexafluoride. Carbon dioxide is particularlypreferred.

Fluoro species usefully employed in the broad practice of the inventioninclude, without limitation, hydrogen fluoride (HF), ammonium fluoride(NH₄F), alkyl hydrogen fluoride (NRH₃F), dialkylammonium hydrogenfluoride (NR₂H₂F), trialkylammonium hydrogen fluoride (NR₃HF),trialkylammonium trihydrogen fluoride (NR₃(3HF)), tetraalkylammoniumfluoride (NR₄F), and xenon difluoride (XeF₂), wherein each R in theaforementioned R-substituted species is independently selected fromC₁-C₈ alkyl and C₆-C₁₀ aryl. Triethylamine trihydrogen fluoride is apreferred fluoro species due to its mild fluorination properties andfavorable solubility in CO₂ when supercritical carbon dioxide SCCO₂ isemployed as the SCF species. Ammonium fluoride is another preferredfluoro species, e.g., in compositions containing co-solvent media, dueto its low toxicity and ease of handling, as well as the acid-basebuffering action associated with the ammonia-HF combination.

Co-solvent species useful in the cleaning compositions of the inventionmay be of any suitable type, including alcohols, amides, ketones,esters, etc. Illustrative species include, but are not limited to,methanol, ethanol, and higher alcohols, N-alkylpyrrolidones orN-arylpyrrolidones, such as N-methyl-, N-octyl-, orN-phenyl-pyrrolidones, dimethylsulfoxide, sulfolane, catechol, ethyllactate, acetone, butyl carbitol, monoethanolamine, butyrol lactone,diglycol amine, γ-butyrolactone, butylene carbonate, ethylene carbonate,and propylene carbonate. Alcohols such as methanol, ethanol andisopropyl alcohol (IPA) are especially preferred.

Inhibitor additives may be used in the compositions of the invention toinhibit attack of the cleaning composition on low dielectric constantlayers. Inhibitor species such as organic acids and/or inorganic acidsare usefully employed for such purpose. Boric acid is a particularlypreferred species.

The relative proportions of the above-described ingredients of thecleaning compositions of the invention can be widely varied to achieve adesired solvating and removal effect in application to photoresist andpost-ashing residue removal from semiconductor wafers.

In general the SCF species comprises a substantial major fraction of thecleaning composition, typically constituting from about 75% by weight,based on the weight of the cleaning composition, to about 99.9% byweight, on the same cleaning composition weight basis. The fluorospecies can be present in a suitable amount in relation to the SCFspecies, and amounts of from about 0.01% by weight to about 5% byweight, based on the weight of the cleaning composition, are usefullyemployed in specific embodiments of the invention. Low k materialattack-inhibitors may optionally be present in an amount of up to about5% by weight, based on the total weight of the composition. Co-solventspecies may optionally be employed in the compositions of the invention,at concentrations of up to about 25% by weight, based on the totalweight of the composition, when employed to increase solubility of thefluoro species in the particular SCF species employed. Surfactants mayoptionally be utilized in compositions of the invention atconcentrations of up to 5% by weight, based on the weight of thecleaning composition. In the compositions including such species, thetotal weight percent of all ingredients is 100%.

In a specific illustrative embodiment, the cleaning composition has thefollowing formulation, wherein all percentages are by weight:

a. Carbon dioxide: 80-99.01% (w/w)

b. Fluoride species: 0.01-5.0% (w/w)

c. Low-k material attack inhibitor: 0.0-5.0% (w/w)

d. Co-solvent: 0-20% (w/w)

e. TOTAL: 100% by weight

In another specific illustrative embodiment, the cleaning compositionhas the following formulation, wherein all percentages are by weight:

a. Carbon dioxide: 80-99% (w/w)

b. Fluoride species: 0.01-5.0% (w/w)

c. Co-solvent: 1-20% (w/w)

d. Surfactant: 0.0-5.0% (w/w)

e. TOTAL: 100% by weight

The pressure of the cleaning composition can be in a range of from about800 to about 10,000 psi, e.g., about 4000 psi, with temperature of thecomposition being in a range of from about 20 to about 150° C., and morepreferably in a range of from about 40 to about 100° C., e.g., atemperature of about 50 to about 80° C.

In an illustrative cleaning process according to the present invention,in one embodiment thereof, the substrate (wafer) to be cleaned is placedin a sealed high-pressure chamber. The chamber then is filled with thecleaning composition of the invention, and the substrate is held underthe cleaning solution for a predetermined time, at predeterminedpressure and temperature, as appropriate to effect the desired cleaningof the substrate. The specific contact time of the cleaning compositionwith the substrate, and process (e.g., temperature and pressure)conditions can be readily determined by simple experiment, based on thedisclosure herein, within the skill of the art.

After the substrate has been subjected to the cleaning composition forsufficient time and at sufficient processing conditions, the substratemay be rinsed with a solution containing only the SCF species, oralternatively containing only the SCF species and optionalco-solvent(s), in order to remove the residue and the fluoro species.After rinsing for a sufficient time to effect appropriate removal of theresidue and fluoro species, the cleaning chamber may be vented and thesubstrate may be removed. Appropriate rinsing conditions can readily bedetermined within the skill of the art, based on the disclosure herein,to achieve a specific removal character and extent.

In another aspect, the invention provides wafer cleaning compositionsutilizing supercritical fluid (SCF) in combination with primary and/orsecondary amine(s).

Such cleaning compositions, utilizing primary and/or secondary amine(s)in the SCF-based cleaning composition, optionally in combination withco-solvent(s), inhibitor(s) and/or surfactant(s), are advantageous forcleaning of photoresists, anti-reflective coatings, metal oxides and/ormetal-containing residues that are present on the semiconductor waferafter plasma etching or ashing.

In such amine-containing SCF cleaning compositions, co-solvent(s) and/orsurfactant(s) are optionally employed to enhance the compatibility ofthe primary and/or secondary amine(s) with the SCF in the composition.The composition can comprise from about 75% to about 99.9% by weight,based on the weight of the cleaning composition, of the SCF, from about0.01% to about 5.0% by weight of the primary and/or secondary amine(s),from about 0% to about 25% by weight of co-solvent(s), and up to about5% by weight of surfactant(s), on the same total composition weightbasis, with all ingredients of the composition totaling to 100 weight %.Compositions of such type may further optionally comprise inhibitorspecies to suppress attack on low k materials that may be present on thewafer being cleaned.

Particularly preferred amine-containing SCF cleaning compositions ofabove-described type include from about 80 to about 99.9% by weight ofSCCO₂, from about 0.01% to about 5.0% by weight of primary or secondaryamine, from about 0% to about 20% by weight of co-solvent, and up to 5%by weight of surfactant, with all ingredient weight percentages beingbased on the total weight of the composition, and with all weightpercentage amounts of such ingredients totaling to 100 weight %.

The SCF in such composition can suitably include any of the illustrativeSCF species described hereinabove. SCCO₂ is a particularly preferred SCFspecies for such purpose. Suitable amines include, without limitation,hydroxylamine (NH₂OH), ammonia (NH₃), alkylamines (R—NH₂) anddialkylamines (R₁R₂NH), wherein R, R₁ and R₂ are each independentlyselected from C₁-C₈ alkyl and C₆-C₁₀ aryl. Co-solvents can be of anysuitable type, including alcohols, amides, ketones, esters, lactones,1,3-diones, etc., with alcohols such as isopropyl alcohol (IPA) beingparticularly preferred. Surfactants likewise can be of any suitabletype, preferably including a non-ionic surfactant such as the non-ionicsurfactants commercially available from Air Products & Chemicals, Inc.under the trademark Surfynol®. Inhibitor(s), when used, can be of a typeas previously described in connection with fluoro species-containing SCFcleaning compositions of the invention.

Amine-containing SCF cleaning compositions of the invention can bedeployed for cleaning at any appropriate supercritical fluid conditionsof temperature and pressure. Typically, such compositions are utilizedat pressure in a range of from about 800 and about 10,000 psi, e.g.,about 4000 psi, and temperature in a range of from about 20 to about150° C., e.g., and more preferably from about 40 to about 100° C.Specific process conditions of temperature and pressure are readilydeterminable within the skill of the art based on the disclosure herein,by simple formulation, varying of process conditions, and determinationof the nature and extent of cleaning thereby achieved, in a particularapplication of the cleaning composition.

The features and advantages of the invention are more fully illustratedby the following non-limiting examples.

FIG. 1 is a scanning electron microscope (SEM) micrograph of apost-ashing trench structure in a two-layer coating on a siliconsubstrate, wherein the two-layer coating includes a first (lower) layerof low k dielectric material and a second (upper) layer of a cappingdielectric material, before cleaning.

FIG. 2 is an SEM micrograph of the trench structure of FIG. 1, afterwashing with a cleaning composition in accordance with one embodiment ofthe present invention. In FIG. 1, the post-ashing residue is visible asa continuous wall covering the trench sidewall. FIG. 2 shows the sametrench structure after cleaning for approximately 2 minutes with acomposition comprising a mixture of about 10% by weight ethanol solutionin SCCO₂, wherein the ethanol solution comprises about 0.5 wt %(C₂H₅)₃N(3HF) and about 0.25 weight % boric acid. A rinsing step followsafter the cleaning step where the trench structure is rinsed in SCCO₂solvent for approximately 5 minutes. Advantageously, the post-ashing(oxidizing or reducing) sidewall residue has been removed, withoutattack on the dielectric materials of the structure. Process conditionsutilized in such embodiment include pressure, temperature and flow rateof approximately 4000 psi, 50° C. and 50 mL/min., respectively.

FIGS. 3A and 3B are scanning electron microscope (SEM) micrographs of apost-ashing trench structure in a two-layer coating on a siliconsubstrate, wherein the two-layer coating includes a first (lower) layerof low k dielectric material and a second (upper) layer of a cappingdielectric material, before cleaning.

FIG. 4 is an SEM micrograph of the trench structure in the two-layercoating on the silicon substrate of FIGS. 3A and 3B, after washing witha cleaning composition in accordance with a further embodiment of thepresent invention. FIG. 4 shows the same trench structure after cleaningfor approximately 2 minutes with a composition comprising a mixture ofabout 10% by weight isopropanol solution in SCCO₂, wherein theisopropanol solution comprises about 0.5 wt % NHF₄, about 0.25 wt %boric acid, and 0.5 wt % surfactant. A rinsing step follows after thecleaning step where the trench structure is rinsed in SCCO₂ solvent forapproximately 5 minutes. Process conditions utilized in such embodimentinclude pressure, temperature and flow rate of approximately 4000 psi,50° C. and 50 mL/min., respectively.

Post-ash residue is clearly visible on the surface of the wafer in FIGS.3A and 3B. FIG. 4 shows that after cleaning the post-ash residue hasbeen removed, with some etching of the dielectric materials. An undercutis visible, which is due to faster etching of the lower (low k)dielectric material.

The micrographs of FIGS. 1-4 thus evidence the efficacy of the cleaningcompositions of the invention, for high efficiency cleaning ofpost-ashing residue on semiconductor wafers.

While the invention has been described herein in reference to specificaspects, features and illustrative embodiments of the invention, it willbe appreciated that the utility of the invention is not thus limited,but rather extends to and encompasses numerous other aspects, featuresand embodiments. Accordingly, the claims hereafter set forth areintended to be correspondingly broadly construed, as including all suchaspects, features and embodiments, within their spirit and scope.

1.-96. (canceled)
 97. A method of cleaning a semiconductor wafer havingresidue thereon, said method comprising contacting the semiconductorwafer with a cleaning composition for sufficient time to remove residuefrom the semiconductor wafer having same thereon, wherein said cleaningcomposition comprises at least one cleaning concentrate and at least onesupercritical fluid and said cleaning concentrate comprises at least onefluoro species and boric acid.
 98. The method of claim 97, furthercomprising forming said cleaning composition by: (a) subjecting at leastone source fluid to pressure and temperature conditions wherein thesource fluid becomes said supercritical fluid; and (b) adding saidcleaning concentrate to the supercritical fluid to produce said cleaningcomposition.
 99. The method of claim 97, wherein the at least one sourcefluid comprises a species selected from the group consisting of carbondioxide, oxygen, argon, krypton, xenon, ammonia, methane, methanol,dimethyl ketone, hydrogen, forming gas, and sulfur hexafluoride. 100.The method of claim 97, wherein the at least one source fluid comprisescarbon dioxide.
 101. The method of claim 97, wherein the at least onefluoro species comprises a fluorine-containing compound selected fromthe group consisting of hydrogen fluoride (HF), ammonium fluoride(NH₄F), alkyl hydrogen fluoride (NRH₃F), dialkylammonium hydrogenfluoride (NR₂H₂F), trialkylammonium hydrogen fluoride (NR₃HF),trialkylammonium trihydrogen fluoride (NR₃(3HF)), tetraalkylammoniumfluoride (NR₄F), and xenon difluoride (XeF₂), wherein each R isindependently selected from C₁-C₈ alkyl and C₆-C₁₀ aryl.
 102. The methodof claim 97, wherein the at least one fluoro species comprisestriethylamine trihydrogen fluoride.
 103. The method of claim 97, whereinthe cleaning concentrate further comprises at least one co-solvent. 104.The method of claim 103, wherein the at least one co-solvent comprisesan organic species selected from the group consisting of methanol,ethanol, isopropyl alcohol, N-alkylpyrrolidones, N-arylpyrrolidones,dimethylsulfoxide, sulfolane, catechol, ethyl lactate, acetone, butylcarbitol, monoethanolamine, butyrol lactone, diglycol amine,γ-butyrolactone, butylene carbonate, ethylene carbonate, and propylenecarbonate, wherein alkyl is C₁-C₈ alkyl and aryl is C₆-C₁₀ aryl. 105.The method of claim 103, wherein the at least one co-solvent comprisesan organic species selected from the group consisting of methanol,ethanol, and isopropyl alcohol.
 106. The method of claim 97, wherein thesupercritical fluid is present in an amount of from about 80% by weightto about 99.01% by weight, based on the total weight of the composition.107. The method of claim 97, wherein the at least one fluoro species ispresent in an amount of from about 0.01% by weight to about 5% byweight, based on the total weight of the composition.
 108. The method ofclaim 97, wherein the boric acid is present in an amount of up to about5% by weight, based on the total weight of the composition.
 109. Themethod of claim 103, wherein the at least one co-solvent is present inan amount of from about 1% to about 20% by weight, based on the totalweight of the composition.
 110. The method of claim 97, wherein thecontacting is carried out at pressure in a range of from about 800 toabout 10,000 psi.
 111. The method of claim 97, wherein the contacting iscarried out at temperature in a range of from about 20 to about 150° C.112. The method of claim 97, wherein the residue comprises materialselected from the group consisting of post-etch photoresist residue andpost-ash residue.
 113. The method of claim 97, further comprisingwashing the semiconductor wafer, at a region at which residue has beenremoved, with a SCF-containing solution to remove post-removal residueand fluoro species from said semiconductor wafer.
 114. The method ofclaim 103, wherein the cleaning concentrate comprises triethylaminetrihydrogen fluoride, boric acid, and at least one co-solvent, whereinthe at least one co-solvent comprises an alcohol selected from the groupconsisting of methanol, ethanol, and isopropyl alcohol.
 115. A kitcomprising, in one or more containers, two or more of the followingreagents for forming a cleaning concentrate: at least one fluorospecies, boric acid, and optionally at least one co-solvent, wherein thekit is adapted to form a cleaning concentrate which is suitable forcombination with at least supercritical fluid.
 116. A composition forcleaning semiconductor wafers, wherein the composition comprises asupercritical fluid, at least one fluoro species, boric acid, and atleast one co-solvent.
 117. The composition of claim 116, furthercomprising residue material.
 118. The composition of claim 117, whereinthe residue comprises material selected from the group consisting ofpost-etch photoresist residue and post-ash residue.